Yes, i am buying bitocoins sometimes for gambling, casue i am very adorable man. But it's so minor amounts like 0,1 or 0,2btc. And it's happening only when my bankroll is done.
everone has its own idea. i m not buying bitcoin because i have no such amout mo moey i am only earning it using signature campaign.If you're earning bitcoin with your signature campaign, you can buy altcoins which have good devs, and people supporting it. This is more cheap investment than buying bitcoin. That's what i'm doing with my earnings from signature campaign. Try it also, you may be successful if you are lucky to pick a altcoin that will become a hype.
The only downside on buying alt coins are it is too risky. But if you can take risk, then it is good. Just do not be depressed if your investment does not grow. It is part of investment especially on a very risky investment like alt coins. I think if you have capital, it is best to invest on bitcoin.
People often buying bitcoin to play some gamble games or just for trading. I can't see more reasons to buy it.
so i think its a good idea as well to start investing in it. 
